The exhaust gas emitted from an internal combustion engine is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NOx”) as well as condensed phase materials (liquids and solids) that constitute particulate matter (“PM”). Catalyst compositions typically disposed on catalyst supports or substrates are provided in an engine exhaust system to convert certain, or all of these exhaust constituents into non-regulated exhaust gas components.
One type of exhaust treatment technology for reducing CO and HC emissions is an oxidation catalyst (“OC”) device. The OC device includes a flow-through substrate and a catalyst compound applied to the substrate. The catalyst compound of the OC device induces an oxidation reaction of the exhaust gases once the OC device has attained a threshold or light-off temperature. One type of exhaust treatment technology for reducing NOx emissions is a selective catalyst reduction (“SCR”) device. The SCR device includes a substrate, where a SCR catalyst compound is applied to the substrate. A reductant is typically sprayed into hot exhaust gases upstream of the SCR device. However, the SCR device also needs to reach a threshold or light-off temperature to effectively reduce NOx. During a cold start of the engine, the OC device and the SCR device have not attained the respective light-off temperatures, and therefore generally may not effectively remove CO, HC, and NOx from the exhaust gases.
One approach for increasing the effectiveness of the OC and the SCR devices involves providing an electrically heated catalyst (“EHC”) device upstream of the OC device and the SCR device. The EHC device includes a monolith and an electrical heater. The electrical heater is connected to an electrical source such as a vehicle battery that provides power to the electrical heater. However, providing power to the electrical heater of the EHC device may deeply discharge the vehicle battery, which in turn impacts battery life. Moreover, as power is supplied to the EHC, the interior and/or exterior lighting of the vehicle may substantially dim due to a voltage drop in the vehicle electrical system. If the vehicle battery has a relatively low state-of-charge (“SOC”), a more pronounced dimming will occur when compared to a vehicle battery that is fully charged. In some instances, the luminosity or intensity of the vehicle lighting may decrease up to about 50%. Accordingly, it is desirable to provide a system that efficiently provides power to the electrical heater of the EHC.